import { useCallback, useEffect, useMemo, useRef, useState } from "react";

import { ThreadComposer } from "@/components/thread/ThreadComposer";
import { ThreadHeader } from "@/components/thread/ThreadHeader";
import { ThreadViewport } from "@/components/thread/ThreadViewport";
import { useNanobotStream } from "@/hooks/useNanobotStream";
import { useSessionHistory } from "@/hooks/useSessions";
import type { ChatSummary, UIMessage } from "@/lib/types";
import { useClient } from "@/providers/ClientProvider";

interface ThreadShellProps {
  session: ChatSummary | null;
  title: string;
  onToggleSidebar: () => void;
  onGoHome: () => void;
  onNewChat: () => Promise<string | null>;
  hideSidebarToggleOnDesktop?: boolean;
}

function toModelBadgeLabel(modelName: string | null): string | null {
  if (!modelName) return null;
  const trimmed = modelName.trim();
  if (!trimmed) return null;
  const leaf = trimmed.split("/").pop() ?? trimmed;
  return leaf || trimmed;
}

export function ThreadShell({
  session,
  title,
  onToggleSidebar,
  onGoHome,
  onNewChat,
  hideSidebarToggleOnDesktop = false,
}: ThreadShellProps) {
  const chatId = session?.chatId ?? null;
  const historyKey = session?.key ?? null;
  const { messages: historical, loading } = useSessionHistory(historyKey);
  const { client, modelName } = useClient();
  const [booting, setBooting] = useState(false);
  const pendingFirstRef = useRef<string | null>(null);
  const messageCacheRef = useRef<Map<string, UIMessage[]>>(new Map());

  const initial = useMemo(() => {
    if (!chatId) return historical;
    return messageCacheRef.current.get(chatId) ?? historical;
  }, [chatId, historical]);
  const { messages, isStreaming, send, setMessages } = useNanobotStream(
    chatId,
    initial,
  );
  const showHeroComposer = messages.length === 0 && !loading;

  useEffect(() => {
    if (!chatId || loading) return;
    const cached = messageCacheRef.current.get(chatId);
    // When the user switches away and back, keep the local in-memory thread
    // state (including not-yet-persisted messages) instead of replacing it with
    // whatever the history endpoint currently knows about.
    setMessages(cached && cached.length > 0 ? cached : historical);
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [loading, chatId, historical]);

  useEffect(() => {
    if (chatId) return;
    setMessages(historical);
  }, [chatId, historical, setMessages]);

  useEffect(() => {
    if (!chatId) return;
    messageCacheRef.current.set(chatId, messages);
  }, [chatId, messages]);

  useEffect(() => {
    if (!chatId) return;
    const pending = pendingFirstRef.current;
    if (!pending) return;
    pendingFirstRef.current = null;
    client.sendMessage(chatId, pending);
    setMessages((prev) => [
      ...prev,
      {
        id: crypto.randomUUID(),
        role: "user",
        content: pending,
        createdAt: Date.now(),
      },
    ]);
    setBooting(false);
  }, [chatId, client, setMessages]);

  const handleWelcomeSend = useCallback(
    async (content: string) => {
      if (booting) return;
      setBooting(true);
      pendingFirstRef.current = content;
      const newId = await onNewChat();
      if (!newId) {
        pendingFirstRef.current = null;
        setBooting(false);
      }
    },
    [booting, onNewChat],
  );

  const emptyState = loading ? (
    <div className="flex h-full items-center justify-center text-sm text-muted-foreground">
      Loading conversation…
    </div>
  ) : (
    <div className="flex w-full max-w-[40rem] flex-col gap-2 text-left animate-in fade-in-0 slide-in-from-bottom-2 duration-500">
      <div className="inline-flex items-center gap-2 text-[11px] font-medium text-muted-foreground">
        <img
          src="/brand/nanobot_icon.png"
          alt=""
          aria-hidden
          draggable={false}
          className="h-4 w-4 rounded-sm opacity-90"
        />
        <span className="text-foreground/82">nanobot</span>
      </div>
      <p className="max-w-[28rem] text-[13px] leading-6 text-muted-foreground">
        Ask questions, continue local work, or start a new thread.
      </p>
    </div>
  );

  return (
    <section className="relative flex min-h-0 flex-1 flex-col overflow-hidden">
      <ThreadHeader
        title={title}
        onToggleSidebar={onToggleSidebar}
        onGoHome={onGoHome}
        hideSidebarToggleOnDesktop={hideSidebarToggleOnDesktop}
      />
      <ThreadViewport
        messages={messages}
        isStreaming={isStreaming}
        emptyState={emptyState}
        composer={
          session ? (
            <ThreadComposer
              onSend={send}
              disabled={!chatId}
              placeholder={showHeroComposer ? "What's on your mind?" : "Type your message…"}
              modelLabel={toModelBadgeLabel(modelName)}
              variant={showHeroComposer ? "hero" : "thread"}
            />
          ) : (
            <ThreadComposer
              onSend={handleWelcomeSend}
              disabled={booting}
              placeholder={booting ? "Opening a new chat…" : "What's on your mind?"}
              modelLabel={toModelBadgeLabel(modelName)}
              variant="hero"
            />
          )
        }
      />
    </section>
  );
}